Introduce OOM reporting to virAsprintf

Actually, I'm turning this function into a macro as filename,
function name and line number needs to be passed. The new
function virAsprintfInternal is introduced with the extended set
of arguments.

tests/nwfilterxml2xmltest.c

@@ -17,6 +17,8 @@
 #include "testutilsqemu.h"
 #include "virstring.h"
 
+#define VIR_FROM_THIS VIR_FROM_NONE
+
 static int
 testCompareXMLToXMLFiles(const char *inxml, const char *outxml,
                          bool expect_error)